(1) Field of the Invention
This invention relates to a method for replacement of existing pipes for replacing cast iron pipes buried in the ground with new pipes, and a device for carrying out the method.
(2) Description of the Prior Art
Many pipelines, for example, such as gas service pipelines for supplying fuel gas, water service pipelines for supplying service water and others, have been laid in the ground. Gas service pipelines have been built by a method in which steel pipes each having a given length are connected with each other through pipe joints such as sockets or welded with each other, or a method in which cast iron pipes are connected with each other through pipe joints.
It is known that it is feared that if strong earthquake force is applied to the above-mentioned gas service pipelines made of steel pipes or cast iron pipes, a part of pipe joints or other parts are broken and so gas leak occurs to cause a big disaster. Therefore, as to gas service pipelines, it is carried out that steel pipes or cast iron pipes are replaced with pipes of synthetic resin having plasticity such as polyethylene and others or steel pipes whether large or small or the numbers of years which have passed since the gas pipelines were constructed.
There is a case where when existing pipes buried in the ground is replaced with new pipes, a method of construction in which a road is open-cut or trenched along existing pipes is employed. However, in this method of construction, there is a case where open-cutting of a road has a wrong effect on circumstances of traffic on the periphery of the road. Accordingly, recently, a method of construction has been proposed in which existing pipes are cut in the longitudinal direction into plural parts and expanded in the radial direction to form a tunnel, and then new pipes are introduced into the tunnel by which the existing pipes are replaced with new pipes.
For example, an art disclosed in Japanese Patent Laid-Open No. 266185 of 1990 (Heisei 2) prior art) relates to "a device for replacing existing pipes with new pipes", which is comprised of a clamping means for pushing inner walls of existing pipes, a notch-forming cutter for forming notches in the axial direction in the inner walls of pipes, a cylinder for traveling which is arranged so as to be able to extend and contract in the axial direction, and a pipe-expanding means for expanding the inner walls of pipes to split the inner walls along the notches, wherein the clamping means, the notch-forming cutter, the cylinder for traveling and the pipe-expanding means are connected with each other to stand in a line, and wherein new pipes are connected with the back portion of the pipe-expanding means. In this art, by operating the cylinder for traveling while pushing the inner walls of pipes through the clamping means, a function part connected with the cylinder for traveling behind the clamping means is traveled while notches are formed in the inner walls of pipes, the pipe-expanding means is moved so as to split the inner walls of pipes along the notches, and at the same times new pipes are introduced into the split inner walls of pipes. Namely, while the notch-forming cutter and the pipe-expanding means are moved forward intermittently into existing pipes in such a manner as a measuring worm, existing pipes are replaced with new pipes. In this art, it is said that it is possible to replace existing pipes with new pipes in one process, and this art can be applied to existing pipes including cast iron pipes. Further, an art disclosed in Japanese Patent Laid-Open No. 238509 of 1994 (Heisei 6) (second prior art) relates to "an cutting and expanding tool", wherein a guide roller and a cutter are mounted on a supporting body along the longitudinal axial line thereof. In this art, bottom portions of main pipes are cut along the axial line of the pipes. Further, when an expander is connected with the supporting body, the main pipes which has been cut by the expander is expanded by the expander to form a tunnel wherein the expanded main pipes function as a roof.
In the first prior art, a plurality of hydraulic machines are used in the clamping means, the cylinder for traveling or the pipe-expanding means. Therefore, there are a problem that since the whole device is necessarily made oversized, this device cannot be applied to existing pipes having small inner diameter, and a problem that although it is possible to replace existing pipes with new pipes in one process, traveling of the device and traveling of new pipes are made in such a manner as measuring worm so that a lot of time is required for construction per unit length.
Particularly, when replacing existing pipes now in use represented by them of gas service pipelines with new pipes, it is indispensable for the replacement of existing pipes with new pipes to be carried out in such a short time that influence upon each home is not exerted seriously. Therefore, it is important how long length of existing pipes can be replaced with new pipes per unit time. Further, in the second prior art, the supporting body is connected with the expander, the supporting body and the expander are arranged into main pipes, and traveled continuously, by which cutting and expanding of the main pipes are carried out. When the second prior art is applied to steel pipes, good results can be got. On the other hand, when the second prior art is applied to cast iron pipes having lower elastic modules as compared with that of steel pipes, there is a problem that splitting of walls of pipes in the axial direction is possible, but main pipes made of cast iron are broken to pieces in an uncontrolled condition when the main pipes made of cast iron are expanded.
Further, in the second prior art, there is a problem that since new pipes are restricted to pipes having outer diameters which allows pipes to be inserted into main pipes which have been expanded along the axial direction, it is impossible to replace existing pipes with a new pipeline having larger outer diameter as compared with that of the existing pipes.
Furthermore, from what inventors of this invention made an experiment, it has become clear that in case of forming grooves in inner walls of cast iron pipes, grooves cannot be formed in inner walls of cast iron pipes merely by rotary cutter being arranged. Namely, in this case, rotary cutters should be driven actively. Therefore, there is a problem that in case of the existing pipes having small inner diameter, rotary cutters cannot be applied for forming the driving system.